Fracking System with Wireline Shifted Ports and  Real-Time Electronic Monitoring System

ABSTRACT

A bridge plug deployed into a wellbore liner of a wellbore is described. The bridge plug includes a packing element and keys, which can be controllable expanded or retracted. The bridge plug is adapted to engage with a downhole tool and cause a sliding sleeve of the tool to open the tool port/s. The bridge plug is run-in on a wireline using a tractor that enables its displacement uphole or downhole. Also, the bridge plug is provided with sensors to monitor the operational parameters in the wellbore and communicate the measured parameters to the surface for enabling operators to monitor and control the downhole operation conditions.

RELATED PATENT APPLICATIONS

This patent Application claims priority form U.S. Provisional Patent Application Ser. No. 62/488,641 filed on Apr. 21, 2017.

TECHNICAL FIELD

The present invention relates generally to oil and gas well completion. More particularly, the present invention relates to a string for use in stimulating multiple intervals of a wellbore.

BACKGROUND

In conventional coil tubing (“CT”) fracking systems, the operator pumps fluid down the annulus between the coil tubing and the casing. Since the coil tubing occupies much of the volume inside the casing, the pumping rate used by the operator is limited. Operators want to achieve over 100 barrels per minute, but the presence of the coil tubing inside the casing limits the pumping rates.

As stage counts increase, “pressure budgets” for a wellbore are being stretched (since every stage in the wellbore acts as a drain on the pressure budget) until at some point, there is not enough pressure available fora given stage to generate meaningful amounts of energy for stimulating and completing that stage. As an operator puts more and more seats in the casing, every seat that the bridge plug passes, needs to have a pressure drop, which in turn means that as the count of seats/stages increases from 40 to 70 and beyond, the operator starts to lose the ability to obtain high pump rates. That is, as the operator starts to run out of pressure-drop budget, and has to start to reducing rates near the toe. A method and apparatus are required to support more stages, while reducing the drain on pressure budget that provides energy for powering operations at each stage.

A frack initiated by an operator at a stage can converge with another frack in a neighbouring stage or well. A method and apparatus for detecting and reporting conditions that indicate the imminence of such an undesirable condition, before it becomes excessively costly to reverse, is required.

In known CT production/stimulation systems, a radially extendable key is provided on a bridge plug to engage a matching profile on the inside of one or more of the sleeves in the production/stimulation tubular, so that when pressure is applied to the bridge plug to push it through the sleeve, the profile engages the key. Upon engagement, the engaged sleeve is actuated by the pressure-exposed plug. In general, the engaged sleeve is moved from a port-closed position covering a port, to a port-open open position exposing the port. After treating a stage, the production/completion operations can be moved to a next stage, by using a tool controlled from surface to retrieve the bridge plug and pull it up-hole to a next stage, using coil tubing. The problem with these systems is that the plug is pulled back up-hole using coiled tubing, which as mentioned above occupies the inner volume of the casing, which in turn reduces pump rates.

Known ball/plug drop completion systems suffer from the problem of erosion of the downhole seats used to catch the balls/plugs. As is understood in the art, progressively smaller seats are used for stages that are closer to the surface. As the seats get smaller, the bridge plugs have more of a tendency to hit critical velocities capable of eroding the seats or the areas just past the seats upon engagement.

Known plug and perf completion systems suffer from the problem of erosion of the perforations in the casing (fluid exit points). When operators perform a plug and perf operation, they try and distribute the fluid entering the formation by shooting an appropriate number of perforations in each stage, to create holes in a casing that generate an appropriate pressure drop. The problem is that if/when sand arrives from the formation through a hole created with the perf gun, the hole tends to get bigger and bigger as it erodes. A perforation that starts out for example, sized at a half-inch in diameter, can grow to the diameter of a Coke can, due to erosion. This means that instead of getting a predictable distribution of pressure across the stages, the pressure becomes very different and very unpredictable from stage to stage. In a lot of cases, there is no even distribution of pressure at all between the stages.

Screen-out is a condition that occurs when the solids carried in a treatment fluid, such as proppant in a fracture fluid, are over-displaced into the formation, thus creating a fluidic bridge across the perforations or similarly restricted flow area. This creates a sudden and significant restriction to fluid flow that causes a rapid rise in pump pressure, which is problematic during fracking operations.

United States Patent Publication No. US2013/0168090 (Themig et al.) assigned to the applicant, describes an actuator tool configured to move through the tubing string that is actuated by wireline, to set a seal in the tubing string to actuate a closure to open a first port, and then to actuate a second closure to open a second port that is uphole from the first port. This can provide an advantage over coiled tubing systems because wireline occupies much less room in the casing than coil tubing, which in turn means the inner volume restriction in the wellbore is far smaller than that created by the coil tubing, which ultimately means that higher pump rates can be supported. One disadvantage of wireline, however, is that sometimes one cannot apply a strong enough force to a wireline cable to pull up a bridge plug to a next stage, since the wireline cable, in certain circumstances, can snap under the massive force that might be required to pull up the bridge plug. A break in the wireline would require the operator to spend time and money using an intervention tool to retrieve or clear away the wireline and the bridge plug, which is costly.

United States Patent Publication No. US2017/218725 (Schnell et al.) assigned to the applicant, describes an actuator dart which is run in on a wireline. The dart has an engagement mechanism adapted to engage a target tool on receipt of ae electrical signal, while dart removal mechanism on the target tool releases the engagement mechanism once the target tool was actuated. The wireline allows for depth determination for appropriately activating the dart inside the tubing string and is also used to send the signal when based in depth measurements. This can provide an advantage over other systems in that the dart can actuate a large number of different tools. As indicated above however, the wireline cable, in certain circumstances, can snap under the massive force that might be required to move the dart inside the wellbore.

SUMMARY

Embodiments described in this specification are directed to a fracking system that uses a treatment string assembly insertable into the inner bore of a wellbore liner, which uses a wireline, rather than coiled tubing. Specifically, a bridge plug attached to a wireline has locking keys for engagement with sleeves of various devices/tools installed in the wellbore for performing the actions needed during various stages of the productions/stimulation processes.

In accordance with a broad aspect of the present invention, there is provided a plug assembly to operate one or more downhole tools installed in a wellbore comprising: a bridge plug with an uphole end and a downhole end, adapted to engage with a target downhole tool; a wireline attached to the uphole end of the bridge plug to transmit bridge plug control signals to and from the bridge plug; and a tractor at the downhole end of the bridge plug, adapted to aid displacement of the bridge plug.

In accordance with another broad aspect of the present invention, there is provided a method for operating a target downhole tool placed in a tubing string in a wellbore, the tool comprising a port and a sleeve covering the port, said method comprising: moving a bridge plug, connected to a wireline extending from surface at its uphole end and a tractor connected at its downhole end, towards the tool; actuating, by a bridge plug control signal received via the wireline, the bridge plug to engage with the sleeve of the target downhole tool; actuating, upon engaging the bridge plug with the sleeve, the bridge plug by hydraulic pressure to displace the sleeve covering the port to open the port; and pumping a fluid through the tubing string and the port for fracking a part of the wellbore adjacent to the bridge plug.

In accordance with another broad aspect of the present invention, there is provided a method of fracking a stage of a tubing string placed in a wellbore, comprising: installing packers to support the tubing string and isolate the stage; installing in the stage a target downhole tool comprising a port and a port covering sleeve; attaching a bridge plug connected at its uphole end to wireline extending to surface, and at its downhole end to a tractor; moving the bridge plug towards the target downhole tool; in response to bridge plug control signals received over the wireline, actuating the bridge plug to engage the port covering sleeve to open the port; displacing the port covering sleeve to open the port; controlling the tractor to retract the bridge plug from the stage; and pumping fracking fluid through the port to frack a formation adjacent to the port.

In accordance with another aspect of the present invention, there is provided a bridge plug for opening a port of a downhole tool installed in a tubing string, comprising: a body with an outer circumferential surface, a downhole end and an uphole end; a packer element at the downhole end enabled to adopt an unset position during run-in of the bridge plug, and a set position for sealing the tubing string after run-in of the bridge plug; at least one key disposed on the outer circumferential surface and enabled to assume a retracted state while moving the bridge plug to the downhole tool, and an expanded state for engagement with a port closure to move a sleeve away from the port after moving the bridge plug to the tool; and a wireline termination attaching the bridge plug to a wireline at the uphole end, the wireline termination adapted to receive at least one bridge plug control signal for driving the packer element into the set position and for releasing the one or more keys in the expanded state.

The system removes or significantly reduces the force applied to the wireline to move a bridge plug from stage-to-stage within the casing/wellbore after a stage is treated by using an alternative mechanism to move the bridge plug further uphole, in the form of a tractor attached and proximate to the bridge plug.

Embodiments described herein provide a production/stimulation system that has at least the following advantages over prior art coil tubing fracking systems known in the art: supporting an unlimited stage count; moving the bridge plug more quickly and efficiently between stages; more easily preventing screen-out and the over-displacement of proppant that often occurs with conventional fracking systems; and significantly reducing erosion of both seats and perforations.

Advantageously, the apparatus and method described herein allow a wellbore treatment system and method that leaves a fully open internal diameter (ID), since protruding seats or stops are not required to stop the plug. Because of the smaller profile of the wireline as compared to coiled tubing, embodiments that employ wireline do not occupy as much of the inner bore of production/fracking tubular (or open hole), and therefore enable higher pumping rates. The bridge plug can be rapidly moved around from stage to stage, without using either coiled tubing or wireline that can snap if exposed to too much pressure, by providing a power source that can generate the force to move the bridge plug in or near the bridge plug itself, as opposed to using force applied from surface.

Furthermore, this system can be used in various borehole conditions, including open holes, vertical holes, straight or deviated holes.

Since the bridge plug uses the wireline, it can also be equipped with parameter-measuring equipment that operates downhole, and then report measured parameters to surface in real time using the wireline as a communication conduit. Moreover, the real-time readings can be correlated to the location of the bridge plug , which is always known by the length of the deployed wireline. This real-time data gives the operator the opportunity to readily anticipate, and thus alleviate the deleterious effects of, screen-out and the over-displacement of proppant.

Some embodiments employ a combination of features described herein to provide a resilient system that supports higher pump rates, an increased number of stages in a wellbore, and real-time parameter measurements which can be used by operators to detect screen-out and the over-displacement of proppant. In addition, the system described herein addresses the issue of erosion, and can create minimum restrictions inside the wellbore as compared with known coiled tubing systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B, also collectively referred to as FIG. 1, illustrate schematic views of a fully cased/lined wellbore, and an open hole wellbore, respectively, with a plurality of deployed downhole tools.

FIG. 2 illustrates an embodiment of a bridge plug deployable in the tubing strings of FIG. 1 by a wireline.

FIGS. 3A and 3B, also collectively referred to as FIG. 3, show engagement of a bridge plug of FIG. 2, with a port closure device of a downhole tool. In FIG. 3A the bridge plug engages the inner surface of the downhole tool, and in FIG. 3B the bridge plug engages the port closure device.

FIG. 4 illustrates the bridge plug opening the ports of the downhole tool to enable fracking.

FIGS. 5A-5C, also collectively referred as FIG. 5, illustrate an exemplary embodiment of the bridge plug with a fluid passage for equalization of pressure in the tubing string.

FIGS. 6A-6C, also collectively referred as FIG. 5, show a sectional view of an exemplary embodiment of the bridge plug showing further details of the fluid passage.

FIGS. 7A and 7B, also referred collectively as FIG. 7, show embodiments of a bridge plug and tractor assembly.

FIG. 8 shows an embodiment of the bridge plug including one or more sensors for measuring downhole conditions of the wellbore.

FIGS. 9A and 9B illustrate an embodiment of the bridge plug including a radio-active densitometer.

DETAILED DESCRIPTION

This disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known starting materials, processing techniques, components and equipment are omitted so as not to unnecessarily obscure the disclosure in detail. Skilled artisans should understand, however, that the detailed description and the specific examples, while disclosing preferred embodiments, are given by way of illustration only and not by way of limitation. Various substitutions, modifications, additions or rearrangements within the scope of the underlying inventive concept(s) will become apparent to those skilled in the art after reading this disclosure. Furthermore, any dimensions provided are provided by way of example and not limitation.

Before proceeding further, it should be noted that terms “uphole”, “downhole”, “back”, “front”, “first”, “second”, “third”, “last” are relative terms, which identify the position of an element with respect to the wellhead (surface), i.e. are used to refer to an element on or closer to the surface side (upwell side) relative to a corresponding feature that is farther from the wellhead (surface). For example, an “uphole” feature generally refers to the feature closer to the wellhead than described element. The terminology “uphole”, “downhole” is also applicable to horizontal wells. Also, the terms “dart” and “plug” may be used interchangeable within this description.

FIGS. 1A and 1B, illustrate schematic views of a fully cased/lined wellbore, and an open hole wellbore, respectively, with a plurality of deployed downhole tools.

FIG. 1A illustrates a schematic view of a wellbore system 100 deployed in a cased wellbore 104. The wellbore system 100 includes a liner 102 that is deployed in the wellbore 104. In one embodiment, the liner 102 is referred to as a casing. An annulus 106 between the liner 102 and the wellbore 104 is cemented for providing support to the liner 102. The wellbore system 100 further includes downhole tools 108 that are strategically deployed in the liner 102 where the formation is to be stimulated. Although, the FIG. 1 illustrates only three downhole tools 108, it is understood that any number of downhole tools can be deployed based on fracking requirement of the wellbore 104.

FIG. 1B shows the wellbore system 200 deployed in an open-hole wellbore 202. The wellbore system 200 includes a tubing string 204, packers 206, and multiple downhole tools 108. The packers 206 are placed around the tubing string 204 in an annulus 202-1 formed between the tubing string 204 and an inner wall of the open-hole wellbore 202 for providing support to the tubing string 204. The packers 206 also isolates different zones to be fractured. Based on the number of zones to be fractured, the tubing string 204 may include multiple stages. For instance, the tubing string 204 of FIG. 1B is divided into three stages, and a downhole tool 108 is deployed in each stage. Although the tubing string 204 shown in FIG. 1B is divided into three stages, it is understood that the tubing string 204 can be divided into a much larger number of stages, depending upon the length of the open-hole wellbore 202. In the embodiment shown in FIG. 1B, each downhole tool 108 has ports and a sliding sleeve enabled to open or close the ports to provide fluids access for a respective completion or production operation, such as a fracking operation. The ports, when opened, provide fluidic communication between an inner bore 110 of the tubing string 204 and the portion of the annulus 202-1 isolated by two consecutive packers 206. The ports in each downhole tool 108 are actuated by a bridge plug conveyed by a wireline not shown in FIG. 1.

FIG. 2 illustrates an embodiment of a bridge plug 302 deployable in the tubing string 204 by a wireline 304. In this embodiment, the bridge plug 302 can be pumped inside the tubing string 204 by fluid pressure. The bridge plug 302 includes a body 310 that forms the housing of the bridge plug 302. The bridge plug 302 includes a packing element 306, and keys 308 placed on an outer circumferential surface of the body 310. The packing element 306 may be provided towards the front or in the back of the body 310 with respect to the keys 308. The keys 308 are disposed around the body 310 and can assume an expanded state, when they protrude radially from the body 310 or a retracted state, when they are retracted inside the body 310 upon application of a force (e.g., a hydraulic or an electric powered force). Similarly, the packing element 306 is adapted to retract (unset position) or expand radially (set position) to engage with the downhole tool 108 present in the tubing string 204. In one embodiment, the bridge plug 302 includes a wireline connector (not shown) attached at the uphole end to receive at least one bridge plug control signal for driving the packer element into the set position and for releasing the one or more keys in the expanded state.

In one implementation, the keys 308 are adapted to expand to engage a shifting sleeve provided in a downhole tool 108. Once the bridge plug 302 engages the downhole tool 108, hydraulic pressure is applied to the bridge plug 302 to open the port provided in the tubing string 204.

FIGS. 3A and 3B show a sectional view of the downhole tool 108 depicting engagement of the bridge plug 302 with the downhole tool 108. In this embodiment, the downhole tool 108 is shown schematically as including a sliding sleeve 404 and a housing 408, the sleeve 404 being a port closure device that can be used by any tool for downhole operations. The housing 408 of downhole tool 108 includes a port 406 that is covered by the sliding sleeve 404 in FIGS. 3A and 3B.

In the embodiment of FIG. 3A, the packing element 306 of the bridge plug 302 is shown in the expanded state, where it grips the internal surface 410 of the housing 408. In the embodiment of FIG. 3B, the packing element 306 is also shown in the expanded state in this case gripping the internal surface 412 of the sliding sleeve 404.

In both embodiments, the sliding sleeve 404 has a shifting profile 402, designed to engage the keys 308 of the bridge plug 302 when the keys 308 are in the expanded state. During engagement, as seen in FIG. 3, the packing element 306 is set, and the keys 308 are expanded into the shifting profile 402 of sleeve 404.

The actuation of the keys 308 to expand from the retracted state to the expanded state is triggered by a plug actuation signal transmitted from surface to the bridge plug 302 over the wireline 304. Similarly, setting of the packing element 306 is activated in response to a packer actuation signal received from the surface over the wireline 304. The keys 308 and the packing element 306 may for example be activated by an electric motor 414 powered and controlled over the wireline 304. The seals of the packing element 306 may engage the respective internal wall 410 of the housing 408 in FIG. 3A, or the internal wall 412 of sleeve 404 in FIG. 3B, by swelling or by a mechanical actuation.

Once the packing element 306 engages the inner surface 412 of the sleeve 404 in response to the packer actuation signal, the plug actuation signal causes the key to expand and hydraulic pressure is applied on the bridge plug 302. This causes the bridge plug 302 and the sliding sleeve 404, engaged by the bridge plug 302, to move and open the ports 406. The open ports 406 enable fracking of the wellbore 104.

The operation of the bridge plug 302 is now described for a fracking operation in connection with FIGS. 1 and 4. The bridge plug 302 can operate in different modes and can be operated to stimulate either one zone or multiple zones of the wellbore 104. Accordingly, such modes of operation are termed as a single-point entry mode or a multi-point entry mode.

In the single-point entry mode, the bridge plug 302 is deployed towards a downhole tool 108 of interest in the tubing string 204. Further, a depth up to which the bridge plug is deployed is based on the distance of that tool from the surface measured as a length of the wireline 304 deployed in the wellbore 104 or 202. For example, let us assume that the first stage is stage 114 shown in FIG. 1. Once the bridge plug 302 arrives at the first stage 114, the packing element 306 of the bridge plug 302 is activated. The keys 308 of the bridge plug 302 are then actuated by to expand and engage the shifting profile 402 of the sleeve 404. The setting of the packing element 306 and the expansion of the keys 308 are controlled with bridge plug control signals received via the wireline 304. In one embodiment, the packing element 306 is controlled with a first bridge control signal received via the wireline 304, and the keys 308 are controlled with a second bridge control signal received via the wireline 304. Thereafter, pressure is applied to the bridge plug 302 to open the port 406 of the first stage 114. FIG. 4 illustrates the situation when the bridge plug 302, engaged with the port closure (sleeve) 404, moved the sleeve 404 from the port covering position shown in FIGS. 3A and 3B, to a port open position.

Next, a fracking fluid is pumped from the surface of the wellbore through the tubing string 204 for fracking the first stage 114 of the wellbore 104, while the bridge plug 302 blocks the fluid flow to stages downhole from the first stage 114. The first stage 114 is fracked by the fluid exiting under pressure through the open ports of the downhole tool 108, as shown at 502 in FIG. 4. Thereafter, the bridge plug 302 is released from the first downhole tool by retracting the keys 308 and disengaging the packing element 306 and is moved to the next stage to be treated, referred to here as the second stage 116, which is uphole from the first stage. In one embodiment, the keys 308 and the packing element 306 are disengaged upon receiving a third bridge plug signal via the wireline 304. The retracted state of the keys 308 and the un-set position of the packing element are also preferable prompted by bridge plug control signals received via the wireline 304. The operation is repeated for the third stage, and any other stages that need to be fracked.

In the multi-point entry mode, the bridge plug 302 is deployed in a first stage 114 of the tubing string 204, to seal the wellbore 104 by setting the packing element 306. The plug engages the sleeve 404 to open the ports 406 as in the single point entry mode. However, instead of fracking the first stage 114, once the port 406 of the first stage 114 was opened, the bridge plug 302 is released from the sleeve 404 of the first stage 114, moved to the second stage 116 and operated to open the ports 406 of the second stage 116. The operation is repeated for the desired number of stages.

In this embodiment, after the bridge plug 302 opens the ports of the last stage of interest, let us assume that is stage 118, the packing element 306 is disengaged from sealing the wellbore 104. Fracking starts with the first stage 114 (most downhole stage of the series of stages to be fracked) stage. Thus, the bridge plug 302 is moved to the first stage 114 and actuated to block the fluid flow beyond the stage in the downhole direction and to engage with the sleeve 404. Thereafter, fracking fluid is pumped from the surface of the wellbore 104 through the tubing string 204 for fracking the all the stages of the wellbore 104 that have the ports open, while the bridge plug 302 blocks the fluid flow to further downhole (i.e., beyond the last stage in the tubing string 204). In this mode of operation, the ports can utilize a flow restriction to create a limited entry of fluid into the formation. The fluid is pumped into the tubing string 204 with high pressure for creating fractures 502 in the wellbore 104 as shown in FIG. 4.

Following completion of the fracture treatment, the pressure in the fracked stages starts to bleed off. Since the bridge plug 302 isolates the uphole portion 504 of the tubing string 204 from the downhole portion 506 of the tubing string 204, when fracking the next zone uphole from the bridge plug 302 starts, a very high-pressure differential may be created across the two ends of the bridge plug 302. Such a large differential pressure may result in the disengagement of the bridge plug 302 from the sleeve 404. This can be a volatile and unstable situation, that if not addressed, can result in the bridge plug accidentally being blown downhole, also causing snapping of the wireline 304. As well, this pressure differential can make it impossible to release the bridge plug for redeployment for treating the next stages, because of the massive amounts of pressure acting in the downhole direction that would need to be controlled before disengaging the bridge plug for further shifting uphole.

Consequently, this large differential pressure needs to be equalized to avoid damaging the bridge plug 302 and wireline 304. The embodiments shown in FIGS. 5A-5C and 6A-6C describe surge prevention solutions to address this pressure differential problem.

One solution, shown in FIGS. 5A-5C, is to provide the bridge plug 302 with an openable fluid passage 602 inside the body 310 to selectively allow equalization of pressure. FIGS. 5A-5C show a view of the bridge plug 302 having an equalization valve 610 provided through the body 310 of the bridge plug 302 with a view to equalize a high pressure in the tubing string 204. In these figures, the valve is shown symbolically at 610 and may be open for pressure equalisation, or closed, as needed. The opening of the valve 610 can be triggered by an electrical signal sent from surface via wireline 304 to the bridge plug 302.

In the embodiment shown in FIG. 5A the bridge plug 302 is in the set position (expanded), sealing the stages downhole from the bridge plug 302. In the set position, the packing element 306 is engaged with the tool of interest, also referred to as the target tool. The keys 308 are in the expanded state, in engagement with the shifting profile 402 of the sleeve 404. After fracking operation, the valve 610 in the bridge plug 302 is triggered to open the fluid-passage 602 to equalize the pressure between the uphole side 604 and downhole side 606. As seen in FIG. 5B, the fluid is allowed to flow from the uphole side 604 to the downhole side 606. It is also desirable to monitor the pressure differential to identity when the equalization has occurred. This can be performed using pressure monitoring sensors in the bridge plug 302, adapted to measure pressure communicate the measurements to the surface using wireline 304. The monitored data is used to trigger the valve 610 to open or close through the wireline 304. The operation of the valve 610 and measurement system for monitoring pressure is described later in connection with FIG. 8.

The valve 610 may be opened in a variety of manners including techniques used to open valves in retrievable packers. For example, If the packing element 306 is a mechanical packing element, the valve 610 can be open by rotating the bridge plug 302. In another example, the valve 610 can be triggered by an electrical signal sent from the surface via wireline 304 to the bridge plug 302. After, the pressure is equalized above and below the bridge plug 302, the packing element 306 can be released as shown in FIG. 5C. Here, the packing element 306 is released, shown by its diameter becoming smaller. Also, the keys 308 are shown as retracted from the previously expanded state shown in FIG. 5B.

FIGS. 6A to 6C show a sectional view of an exemplary embodiment of the bridge plug 302 with the valve 610 in some details. In this example, the valve 610 include a valve body 704 and an internal seal 706. The valve 602 is placed in the fluid-passage 602 formed throughout the bridge plug 302, as discussed in connection with FIGS. 5A-5C. In the embodiment of FIG. 6A, the valve 610 is closed, as the internal seal 706 is caught, for example, a bore 710 formed in an inner wall 708 of body 310 of the bridge plug 302. No fluid can pass through the fluid passage 602 past the internal seal 706.

When the valve 610 is open, the internal seal 706 is moved out of the bore 710, opening the fluid passage 602. For example, the internal seal 706 may be moved towards downhole direction until the internal seal 706 disengage from the inner wall 708 of the bridge plug 302. Thereafter, the fluid is allowed to flow through the fluid-passage 602 as shown in FIG. 6B. After the pressure of fluid is equalized between the uphole and downhole sides of the bridge plug 302, the bridge plug 302 is released from the sleeve/inner wall of the downhole tool 108 of the current stage, and the keys 308 are retracted from the profile 402, and as shown in FIG. 6C.

In some embodiments, the bridge plug 302 may include motion dampers to prevent sudden motion of the bridge plug caused by pressure surges. Such motion dampers may also assume a retracted state or an expanded state. The dampers may be deployed by sending a signal to the bridge plug 302 over the wireline 304 or may be deployed automatically under the influence of a centrifugal force. An exemplary implementation of the such motion dampers is explained with respect to FIGS. 7A and 7B.

FIGS. 7A and 7B show an embodiment of the bridge plug 302 with motion dampers, such tractor 804 including tracked wheels 802 attached to the bridge plug 302. In one implementation, the wheels 802 are disposed around the bridge plug 302. The wheels 802 are retractable and adapted to engage and disengage with the inner wall of the tubing string 204, to control movements of the bridge plug 302. The wheels 802 may be actuated to engage the inner wall of the tubing string 204 by an electrical motor controlled from the surface, or autonomously.

Thus, the wheels 802 may be activated (i.e., expanded or retracted) by an electrical motor controlled by a signal provided from the surface via wireline 304. In this embodiment, the bridge plug 302 is initially pumped in the tubing string 204 with the wheels 802 in the retracted state. The wheels 802 are deployed after the tractor control signal is communicated from the surface through the wireline 304. The resulting friction between the wheels 802 and the inner wall of the tubing string 204 will reduce/dampen the speed of the bridge plug.

Autonomous deployment of the wheels 802 may be triggered by the centrifugal force or by the speed of the plug in the tubing string 204. For example, the centrifugal force generated when the bridge plug spins in the tubing string, may be used to trigger expansion of the wheels 802 from the retraced position, so that the centrifugal force is rapidly transferred to the inside surface of the tubing string 204 thus increasing friction between the wheels 802 and the inside of tubing string thus controlling the spinning of the plug.

The wheels 802 may also deploy automatically when the uphole speed of the bridge plug 302 exceeds a predetermined threshold. In one example, the threshold speed of the bridge plug 302 is 1 m/s. In one embodiment, surface of the wheels 802 are made of rubber or a milled metal, and the contact surface of the wheels can be ½ an inch wide.

In an alternative embodiment, the wheels 802 can be attached to the tractor 804 attached to the bridge plug 302 as shown in FIG. 7A. The tractor 804 is connected to the bridge plug 302 by any known means. The tractor 804 is powered by an electrical current through the wireline 304 and can be moved in both directions in the tubing string 204. Displacement of the tractor 804 inside the tubing string is controlled by tractor control signals received over the wireline 304. In this embodiment movement of the bridge plug 302, which is connected to the tractor 804, is attenuated and controlled by the tractor 804. In another embodiment, the tractor 804 can be integrated into the bridge plug 302. The tractor 804 limits uncontrolled downhole movement, as well as uphole movement of the bridge plug 302 in the tubing string 204.

The bridge plug 302 can also be used to measure downhole conditions, such as temperature, pressure, sand concentration, etc. in real time. In one example, the bridge plug 302 may include an array of sensors to monitor downhole conditions. An exemplary implementation of the such monitoring is explained with respect to FIG. 8.

FIG. 8 illustrates an embodiment of the bridge plug 302 including one or more sensors 902, 904. The one or more sensors 902 may include, but are not limited to, a pressure sensor, a densitometer, an acoustic sensor, and a temperature sensor. In the illustrated embodiment, the sensors can be coupled to the bridge plug 302 at the uphole end of the plug, as shown by sensors 902, and at the downhole end of the bridge plug 302, as shown by sensors 904. The terms “uphole end” and “downhole end” of the bridge plug refer here to the placement of the sensors when the plug is run into the wellbore. Preferably, pressure and temperature sensors may be placed at both the uphole and downhole ends to measure these parameter in the uphole portion 504 and downhole portion 506, shown on FIG. 4. Listening devices may also be provided at any or both uphole and downhole ends. A radioactive densimeter is preferably placed at the uphole end. It is to be mentioned that other types of sensors 902, 904 may be used, the above types of sensors were indicated by way of example.

The sensors 902, 904 sense the downhole parameters of interest and communicate to the surface of the wellbore system 100 via wireline 304 or wirelessly (the wireless mode is not illustrated). For instance, the pressure sensor measures real-time pressure at the bridge plug 302 near a fracking or production port. In another example, the temperature sensor measures temperature readings of fracking fluid near the bridge plug 302, and communicates the measured reading to the surface. In one embodiment, the measured temperature reading indicates how rapidly the fluid is circulating from the surface (where the water might be heated) to the downhole location of the bridge plug 302. In another example, the acoustic sensor measures acoustic readings that denotes geological fracture events such as the merger of two separately initiated fracks, or equipment breakdown events, and communicate to the surface. In another example, the densitometer measures concentration of sand near the bridge plug 302 and communicates the measurement to the surface.

Generally, the fluid for fracking the wellbore 104 includes proppant that enables fracking operations. The proppant mixed with the fluid is pumped through the tubing string 204. A radio-active densitometer sensor can be used to detect over-displacement and screen-out by measuring the density of the slurry generated during fracking the wellbore 104 using radiation measurements.

In one embodiment, the radio-active densitometer may be used to measure concentration of the sand near the bridge plug 302. The radio-active densitometer may also detect sand-laden fluid at the bridge plug 302 as shown in FIG. 9A, and report to surface via the wireline 304. The radio-active densitometer sends information to the surface about screen out and over displacement conditions with complete location and timing information, just as either condition begins to materialize. FIG. 9A shows the sand concentration at the bridge plug 302 is high, so the pumping of proppant is stopped or reduced, thus, the screen out and over displacement conditions are avoided. FIG. 9B shows the sand concentration at the bridge plug 302 is low after halting the pumping of proppant.

The readings are communicated to the surface and if the concentration of the sand crosses a threshold value, pumping of proppant is stopped to avoid displacement of the proppant. For example, if a sand concentration of 4 lbs/gallon is suddenly detected by the radio-densitometer near the bridge plug 302, a signal is communicated to the surface via the wireline 304 in real time, and pumping of proppant is reduced or suspended to avoid over-displacement. Furthermore, in response to this reading, the operator can cause the bridge plug 302 to be moved uphole from this high sand concentration zone based on the measured sand concentration, and another stage of the wellbore with lower sand concentrations can be operated upon. Screen-out conditions that are very costly can thus be avoided through such real-time detection, communication to surface, and remediation, of conditions around the bridge plug 302.

The densitometer can also provide useful information that can be used to detect not only screen-out and over-displacement, but also other problematic conditions by detecting the presence of radioactive tracers near the bridge plug 302, that are originally inserted in the fluid before pumped into the tubing string 204 from the surface. Further, the radioactive tracers measurements may be associated with a certain location in the casing/wellbore at which the tracers were detected.

As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, product, article, or apparatus that comprises a list of elements is not necessarily limited only to those elements but may include other elements not expressly listed or inherent to such process, product, article, or apparatus. Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

Additionally, any examples or illustrations given herein (including in any Appendix) are not to be regarded in any way as restrictions on, limits to, or express definitions of, any term or terms with which they are utilized. Instead, these examples or illustrations are to be regarded as being described with respect to one particular embodiment and as illustrative only. Those of ordinary skill in the art will appreciate that any term or terms with which these examples or illustrations are utilized will encompass other embodiments which may or may not be given therewith or elsewhere in the specification and all such embodiments are intended to be included within the scope of that term or terms. Language designating such nonlimiting examples and illustrations includes, but is not limited to: “for example,” “for instance,” “e.g.,” “in one embodiment.”

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component.

Reference throughout this specification to “one embodiment”, “an embodiment”, or “a specific embodiment” or similar terminology means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment and may not necessarily be present in all embodiments. Thus, respective appearances of the phrases “in one embodiment”, “in an embodiment”, or “in a specific embodiment” or similar terminology in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics of any particular embodiment may be combined in any suitable manner with one or more other embodiments. It is to be understood that other variations and modifications of the embodiments described and illustrated herein are possible in light of the teachings herein and are to be considered as part of the spirit and scope of the invention.

In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that an embodiment may be able to be practiced without one or more of the specific details, or with other apparatus, systems, assemblies, methods, components, materials, parts, and/or the like. In other instances, well-known structures, components, systems, materials, or operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the invention. While the invention may be illustrated by using a particular embodiment, this is not and does not limit the invention to any particular embodiment and a person of ordinary skill in the art will recognize that additional embodiments are readily understandable and are a part of this invention.

Although the invention has been described with respect to specific embodiments thereof, these embodiments are merely illustrative, and not restrictive of the invention. Rather, the description is intended to describe illustrative embodiments, features and functions in order to provide a person of ordinary skill in the art context to understand the invention without limiting the invention to any particularly described embodiment, feature or function. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the invention in light of the foregoing description of illustrated embodiments of the invention and are to be included within the spirit and scope of the invention. Thus, while the invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the invention. 

What is claimed is:
 1. A plug assembly adapted to operate one or more downhole tools installed in a wellbore, comprising: a bridge plug with an uphole end and a downhole end, adapted to engage with a target downhole tool; a wireline attached to the uphole end of the bridge plug to transmit bridge plug control signals to and from the bridge plug; and a tractor at the downhole end of the bridge plug, adapted to regulate the displacement of the bridge plug.
 2. The plug assembly of claim 1, wherein the tractor includes: a motor operated through tractor control signals; and at least two wheels adapted to displace the tractor when driven by the motor.
 3. The plug assembly of claim 2, wherein the wheels are retractable and extendable.
 4. The plug assembly of claim 1, wherein the tractor is an integral part of the bridge plug.
 5. The plug assembly of claim 1, wherein the tractor is attached to the downhole end of the bridge plug.
 6. The plug assembly of claim 2, wherein the wheels are actuated to engage an inner surface of a tubing string in response to a tractor control signal received over the wireline.
 7. The plug assembly of claim 2, wherein the wheels are autonomously actuated to engage an inner surface of a tubing string.
 8. The plug assembly of claim 2, wherein the wheels, when expanded, move along an inner surface of a tubing string in the uphole direction in response to tractor control signals received via the wireline.
 9. A method for operating a target downhole tool placed in a tubing string in a wellbore, the tool comprising a port and a sleeve covering the port, said method comprising: moving a bridge plug, connected to a wireline extending from surface at its uphole end and a tractor connected at its downhole end, towards the tool; actuating, in response to a bridge plug control signal received via the wireline, the bridge plug to engage with the sleeve of the target downhole tool; actuating, upon engaging the bridge plug with the sleeve, the bridge plug by hydraulic pressure to displace the sleeve covering the port to open the port; and pumping a fluid through the tubing string and the port for fracking the part of the wellbore adjacent to the bridge plug.
 10. The method of claim 9, wherein moving the bridge plug towards the tool comprises controlling the tractor, by tractor control signals received via the wireline, to move the bridge plug.
 11. The method of claim 9, wherein the method further comprises: actuating, in response to a first bridge plug control signal received via the wireline, a packing element of the bridge plug to engage with the sleeve of the target downhole tool; and actuating, in response to a second bridge plug control signal received via the wireline, at least one key of the bridge plug to engage with a profile in the sleeve of the target downhole tool.
 12. The method of claim 11, wherein method further comprises: disengaging, by a third bridge plug control signal received via the wireline, the packing element and the at least one key of the bridge plug from the target downhole tool; extending, by a first tractor control signal received over the wireline, a pair of wheels of the tractor from a retracted position to an extended position to enable movement of the bridge plug in the tubing string; actuating, by a second tractor control signal received over the wireline, the tractor for moving the bridge plug in an uphole direction in the tubing string.
 13. A method of fracking a stage of a tubing string placed in a wellbore, comprising: installing packers to support the tubing string and isolate the stage; installing in the stage a target downhole tool comprising a port and a port covering sleeve; attaching a bridge plug connected at its uphole end to wireline extending to surface, and at its downhole end to a tractor; moving the bridge plug towards the target downhole tool; in response to bridge plug control signals received over the wireline, actuating the bridge plug to engage the port covering sleeve to open the port; displacing the port covering sleeve to open the port; controlling the tractor to retract the bridge plug from the stage; and pumping fracking fluid through the port to frack a formation adjacent to the port.
 14. The method of claim 13, wherein moving in the bridge plug towards the target downhole tool comprises using both the wireline and the tractor to regulate displacement of the bridge plug.
 15. The method of claim 13, wherein controlling the tractor to retract the bridge plug from the stage comprises: on receipt of a first tractor control signal received over the wireline, extending a pair of wheels of the tractor from a retracted position to an extended position, to enable displacement of the pair of wheels along a wall of the tubing string; on receipt of a second tractor control signal, driving the tractor with the bridge plug in an uphole direction in the tubing string.
 16. A bridge plug for opening a port of a downhole tool installed in a tubing string, comprising: a body with an outer circumferential surface, a downhole end and an uphole end; a packer element at the downhole end enabled to adopt an unset position during run-in of the bridge plug, and a set position for sealing the tubing string after run-in of the bridge plug; at least one key disposed on the outer circumferential surface and enabled to assume a retracted state while moving the bridge plug to the downhole tool, and an expanded state for engagement with a port closure to move a sleeve away from the port after moving the bridge plug to the tool; and a wireline termination attaching the bridge plug to a wireline at the uphole end, the wireline termination adapted to receive at least one bridge plug control signal for driving the packer element into the set position and for releasing the one or more keys in the expanded state.
 17. The bridge plug of claim 16, further comprising a motor for controlling operation of the packing element to assume the set position and the unset position in response to the bridge plug control signals.
 18. The bridge plug of claim 16, further comprising a motor for controlling operation of at least one key to assume the expanded state and the retracted state in response to the bridge plug control signals.
 19. The bridge plug of claim 16, wherein the body further comprises: a fluid passage between the uphole end and the downhole end, for enabling, equalization of fluid pressure on the uphole side of the bridge plug with the fluid pressure on the downhole side of the bridge plug, when the packing element is in the set position and the at least one key is in the expanded state; and an equalization valve placed in the fluid passage to selectably allow fluid flow through the fluid passage in response to a control signal received over the wireline.
 20. The bridge plug of claim 16, further comprising at least two wheels provided on the outer circumferential surface, adapted to engage and disengage with an inner wall of the tubing string, to control movement of the bridge plug in the tubing string, wherein the at least two wheels are powered from current received on the wireline.
 21. The bridge plug of claim 16, further comprising one or more sensors configured to obtain measurements for any one or more of pressure, temperature, radioactivity and sand concentration near the respective uphole and downhole end of the bridge plug and to transmit the measurements over the wireline.
 22. The bridge plug of claim 21, wherein the measurements are correlated to a location measurement of the bridge plug. 